1. Field of the Invention
The present invention relates to apparatus and methods for coupling an input optical fiber selectively to one of a plurality of output fibers. In particular, the present invention is a 1xc3x97N fiber switch.
2. Description of the Prior Art
Currently, there are a number of ways to implement fiber-to-fiber switches, where an input optical fiber is coupled selectively to one of a plurality of output fibers. A first method involves bringing the cut and polished surface of the input fiber into close proximity to the similarly cut and polished end of the desired output fiber. If the fibers"" cores (where the light is guided) are positioned closely and accurately enough, most of the light from the input fiber will enter the core of the output fiber. This kind of switch requires accurate positioning of the fibers to a fraction of a micron, if low losses and achievability are to be accomplished.
A second switching method involves collimating the light from the input fiber using a lens. The collimated beam is then reflected into a collimator and hence directed into the desired output fiber using a movable mirror. Each output fiber has its own collimator. This type of switch requires each output fiber-collimator to be aligned to a very small fraction of a degree in order to maintain sufficiently low-loss coupling. In addition, the mirrors must accurately reproduce the same output beam angle for each output fiber.
A third type of switch involves passing the light from the input fiber through an interferometer with two possible outputs, such as a Mach-Zender interferometer. By manipulating the path length of one arm of the interferometer, the input light is directed to either of the two possible outputs. Free-space or fiber interferometers are expensive and must remain stable to a small fraction of a wavelength. Waveguide interferometers require very accurately positioned couplers in order to efficiently couple light from fibers to the waveguide switch and back to the fiber.
To summarize, all of the known 1xc3x97N switching methods require high precision alignment of a number of their optical components. When such switches are to be used with single mode fibers, as are used in optical networking, the required precision of the switch components exceed the accuracy achieved by normal manufacturing processes. Therefore, expensive and time consuming active alignment is required for each output fiber, often in several stages.
A need remains in the art for a 1xc3x97N optical fiber switch which does not require active alignment steps for each output fiber.
An object of the invention is to provide 1xc3x97N optical fiber switches which do not require active alignment steps for each output fiber. A 1xc3x97N optical switch according to the present invention switches between output fibers by utilizing two beam deflecting elements, for example first passing the input beam through a translating element and then through a beam angle adjusting element. The translating element directs the input beam toward the selected fiber, and the angle adjusting element directs the beam toward the core of the selected fiber. Alternatively, both of the deflecting elements could be angle adjusting elements, or the first element could be an angle adjusting element and the second element a translation element.
The translation element preferably includes beam translating block comprising a plane parallel block of an optical material, such as glass. A perpendicular rotating motor rotates the block about an axis perpendicular to the input beam direction. A gimbal ring and axial motor rotate the block and perpendicular motor about the longitudinal axis of the switch. The effect of the Beam Translator, when correctly positioned by the two motors, is to cause the input beam to be translated to a selected off-axis position.
The angle adjusting element preferably comprises two wedge prisms (for example Risley prisms) and associated motors. Each prism is independently rotated by its motor. The prisms change the angle of an incident light beam. Thus, by adjusting each prism appropriately, the input beam can be deflected in any direction and at any angle from 0xc2x0 up to twice the angle achievable by each prism alone. The angle adjusting element could also be an adjustable liquid prism.